Since the other night My 1986 F150 300 inline non-feedback carb will Crank over and will start if I pour fuel down the carb, which has kind of been a repeat problem. I’ve owned the truck since Spring 2023 and I’ve put about 1000 miles on it hauling loads to and fro.


Since buying the truck, it would run for a couple of tanks and then it would quit. I’d also find grey sand-like sediment caught in the clear filters I’d run on the truck, like this:


I’ve replaced a the fuel pump twice, most recently when I overhauled the fuel system and successfully drove the truck about 15 miles before it died on the highway.

Fuel system overall:
1) dropped tank, wiped out with paper towel
1.5) ran compressed air through the fuel sending unit
2) ran brand new thick 3/8” ID fuel hose from the tank up to pre-filter before lift pump
3) brand new motorcraft spam can inline filter
4) new fuel pump
5) hardline delete and swapped to new 3/8 soft hose
6) running mesh filter glass pre-carb fuel filter so I can see if fuel is flowing
7) 6 month old Amazon carb that might be gummed up with the sediment in the earlier pictures.

the truck was running just fine for about 15 miles like this before it seemed like fuel was no longer getting to the carb.

my thoughts are

1) replace the carb again
2) replace the fuel sending unit
3) maybe a fuel check valve somewhere
4) delete the mechanical lift pump and go with a e pump and a fuel pressure regulator

any ideas?

 

I never liked soft hose running all the way from the tank. I have seen it cause problems, and the factory never did it that way. I would keep the amount of hose in the system the least amount possible,

 

I see a few things I dont like and like DaveF that rubber fuel line from tank to the front.
Let me back up you dropped the tank but did not replace it, that sandy stuff can only be coming from the tank now that everything else is changed.
The top of the tank can have that stuff. My tanks looked great when looking in the sender holes. I found vary fine rust in the filters (I run 1 like like yours and a screw in the carb one) and the carb bowl it could only come from the top of the tanks.

The fuel line is not 3/8" but 5/16".
I say this because I could not get a 3/8 hose to not suck air going into a can up on the inner fender when hooked to the motor driven fuel pump, eve with 2 clamps.
Get a coil of 5/16 copper / nickle tubing to go from the tank forward. Get new 5/16 rubber hose to hook the tubing to the tank, tubing to fuel pump.

I would pull the carb and get a rebuild kit and clean it as I am sure it has sand in it.
You may want to drop the tank again to see what the inside looks like to make sure it is clean and go from there.

With the above done I am pretty sure you will not have any issues again.
You can also try running the motor off a small gas can set up on the inner fender with a long 5/16 hose to the pump.
Dave ----

ps try getting your gas at a different station as that one could have bad gas that you are getting.

 

Do you have dual tanks?
The rear tank is the normal tank. The fuel selector is energized to use the front tank.
Jim

 

Just in time I'm fixing to work on my dual tank F150 and thought the operation is just opposite of this. Now I need to get the manual and start the trouble shooting.

 

Edd you may want to start your own thread as the fuel systems are different through out the years and motors used.
The system for the 300 six stayed the same 80 - 86 and is the easy one but all others can be a real mess of what was used between where the fuel pumps are how many , filters and tank switches.

Then you get into what each motor used for spark and fuel.
Dave ----

 

Dave I do recall that you had good results going from a 3/8" to a 5/16" fuel line but I've always wondered why a fuel line that is 1/16" larger diameter would hurt fuel flow? I wonder if there was another issue besides the slightly larger fuel line that was somehow solved simultaneously with the down sizing of the fuel line to 5/16", which is the stock size you said.

Service manuals always say have a half full tank to help prime the fuel system after working on it.

 

Tank is full. I think the sizing issue is right but not sure.


I switched to a clear nylon hose and ran that into a jerry can. Fuel pump was pulling and pushing fuel. The truck even stayed running for awhile, albeit roughly.


I thoug

I thought this was interesting. Clean gas came out of the jerry can but dirty after it leaves the brand new fuel pump


not sure what the discoloration could be but the truck did run like this for about 5 minutes.


so after that I switched back to the New 3/8” black soft line that we don’t like and the truck ran for a couple of minutes before shutting off.

I’ll find a smaller ID and OD line to switch to instead

 

btw there is gas in that clear fuel line in the zoomed out photo



So I’m very confused about the gas discoloration

 

I think this is precisely the problem now.

yes I did drop and clean the tank out as far as my arm could reach on the top, sides, and bottom






the tank looked remarkably clean and rust free

 

See picture 3, post 8
The fuel inlet to the carb is the threaded connection closest to the passenger fender.
The one with the nipple in the photo, closest to the valve cover in the vent for the float bowl.
Which one are you using... Which one is connected to the fuel pump???
Good luck
Jim

 

Sure enough, he doesn't have a hose nipple on there does he? Or more than likely it takes one of those screw on metal fuel filters.

 

The screw in fuel filter looks like this.
https://www.ford-trucks.com/forums/1...wont-seal.html

 

IIRC, he discovered the larger flex hose was not sealing properly to the rigid tubing. Because the line between the tank and pump is not pressurized, fuel did not leak out. But it is under a light vacuum with the engine running, so air would get sucked in, reducing the volume of fuel reaching the carb. The harder the pump tried to draw fuel, a greater amount of air got pulled in.

 

It's for that reason also I do not like long runs of rubber hose. Sometimes the hose tends to be oval instead of round when they wrap the hose tight around the reel at the store. This makes it even more prone to sucking shut when the pump is pulling fuel from the tank.